The present invention relates generally to asphalt roofing products, including asphalt for Built Up Roofing Asphalt (BURA). More particularly the present invention relates to methods and compositions for producing BURA coating asphalt compositions from non-coating grade asphalts, such as paving-grade asphalts.
Asphalt compositions suitable for BURA are generally produced by selecting a suitable asphalt, or asphalt flux, and processing the asphalt to obtain particular properties useful for a BURA. For instance, it is important that the asphalt in roofing products retain some degree of hardness and do not flow under conditions of high temperature. Such an increased hardness is generally accompanied by a reduced penetration level, an increased viscosity, and an increased softening point and reduced ductility.
One way in which the asphalt may be processed consists of air blowing, which is an oxidation process that involves blowing air through molten asphalt to modify the physical properties of the asphalt. In such an air blowing process, air is blown through an asphalt flux for a particular period of time at an elevated temperature. The air blowing asphalts process generally raises the softening point of the asphalt, which increases the shingles' ability to resist flowing at high temperatures on a roof, allows for the application of the asphalt on the roof by mopping or mechanical application and creates a BURA that will perform over many years on the roof in spite of being exposed to sun, high temperatures, and inclement weather conditions.
Conventional asphalt compositions used for BURA incorporate special “asphalt roofing flux” asphalt as the feedstock to the air blowing process in order to meet the desired properties for a roofing application. Such asphalt roofing flux often comprises materials that are naturally softer (higher penetration, lower viscosity) than paving grade asphalts, which are considered “hard” asphalts. Unfortunately, such coating grade asphalts are in short supply and may be costly compared to many other types of asphalts, particularly, commodity hard asphalts.
There has been an effort to provide a broader range of asphalt feedstocks for use in roofing products to improve the supply security and decrease the cost of shingle production. For example, U.S. Pat. No. 4,554,023, the disclosure of which is incorporated by reference herein in its entirety, discloses the use of a bis-stearoylamide additive to reduce the viscosity of the asphalt to a viscosity desired for the ultimate blend. Additionally, U.S. Pat. No. 7,951,239, the disclosure of which is incorporated by reference herein in its entirety, discloses a method for producing coating asphalts from paving grade asphalt feedstocks. The method includes partially air blowing the paving grade asphalt feedstock to lower its penetration value and raise its softening point. A wax is then added to the partially blown asphalt to further raise its softening point to a point that is within the desired range for a coating asphalt. This process additionally incorporates a blowing catalyst, such as phosphoric acid to further soften the asphalt. Although this process produces suitable coating-grade asphalt, the incorporation of a solid wax additive into a molten asphalt composition greatly increases the processing costs, since such cannot be done on existing processing lines. Additional processing modifications may include providing proper storage of the phosphoric acid blowing catalyst.
Therefore, there remains a need for a process that expands the potential asphalt feedstock compositions for producing coating asphalt compositions that incorporates hard asphalt, such as paving grade asphalt, that is compatible with current processing lines and does not increase coating asphalt compositions' manufacturing costs.